Calculating Motive Power Requirements
For some reason my replies aren’t getting posted, so here is the text of the reply to Tim’s ‘rule of thumb’ method of assigning motive power to trains.
I found an article in the November 1978 Model Railroader on tractive effort, horsepower, grades, etc. for both prototype and model railroads. The article describes a method for scaling those forces down for practical operations on a model railroad. The conclusions are similar to yours, Tim. The ruling grade on my layout is 2% in the helix. Based upon staging track capacity, mainline freight trains are limited to a maximum of 28 cars plus ABBA F units while passenger trains are limited to 14 cars plus AA E units. The A/D track in the yard can accommodate 20 cars, so trains terminating in the yard are limited to that number.